Counter rotating packerheads for concrete pipe making machines are known in the art. Counter rotating packerheads with a vibrator disposed below the packerhead are also known in the art. However, no design taught by the prior art effectively combines the benefits provided by counter rotating packerhead technology with vibrator technology to provide a concrete pipe making machine that produces high quality pipe at high production rates.
U.S. Pat. No. 4,540,539 discloses a counter rotating packerhead with an upper roller assembly and a lower longbottom assembly disposed below the upper roller assembly for use in dry cast pipe production. This radial distribution process is also known as concrete forming. The upper roller assembly acts to initially distribute the dry cast concrete radially outward through a wire reinforcing cage against a concrete pipe mold. After the dry cast concrete is initially pressed against the cage and mold by the upper rotating roller assembly, the lower rotating longbottom assembly further presses the dry cast concrete against the cage and mold.
The upper roller assembly and lower longbottom assembly of U.S. Pat. Nos. 4,540,539 and 5,080,571 counter rotate, that is, they are driven in opposite directions. The rotation of each assembly, if viewed without regard to the presence of the other assembly, would act, or tend to act, to impart a twist to a wire cage which is contained within the concrete structure. However, in actual operation, the imposition of the counter clockwise and the clockwise twists are occurring simultaneously and may, at any given instant in time, overlay one another with respect to the points of application of the twists to the wire cage so that the forces effectively cancel out one another at all times. The elimination of cage twist significantly improves the final product because cage twist causes voids in the concrete and voids significantly weaken the final concrete pipe product.
The problem primarily associated with counter rotating packerheads is low pipe density. Attempts to cure this defect resulted in the first combination counter rotating packerheads/vibrator concrete pipe making machines.
U.S. Pat. No. 4,957,424 discloses a counter rotating packerhead with a vibrator disposed below the packerhead. This patent is said to represent an improvement over methods of concrete pipe making that include a counter rotating packerhead only or a vibrating core only. The earlier methods that implemented vibrating cores only produced a high density concrete pipe because the vibration process is very effective in consolidating or densifying dry cast concrete. However, the vibration process is quite slow and has its own disadvantages. Further, this machine is only capable of producing one pipe at a time.
Concrete pipe making methods that employ vibrators only are subject to slumping problems unless carefully contracted. The voids and other distortions (also referred to as concrete-slumping) are primarily caused by the volume reduction of the concrete after the vibration. Vibration causes dry cast concrete to densify which results in a reduction in volume. The reduction in volume will result in void spaces around the form work, especially at or near the wire reinforcing cages.
In rising core concrete pipe making machines taught in the prior art, the density levels attainable in the pipe are limited. If the vibrational frequency is increased to too high a level, concrete-slumping, void spaces and other distortions will be present in the finished pipe. This is especially problematic in irregularly shaped pipes, such as pipes with top spigots, tongue joints and grooved gasket joints. Unsatisfactory pre-packing before vibration will cause concrete-slumping, especially in forms used to make the above-noted irregularly shaped pipes. Pre-packing using weighted forming rings has been tried but manufacturers then encounter problems with length control. If the pipe lengths and joints do not meet specifications, the pipes will be rejected.
The U.S. Pat. No. 4,957,424 states that exposing the dry cast concrete to a counter rotating packerhead and vibration combines the advantages of vibration with the speed of counter rotating packerheads. Thus, the invention disclosed in U.S. Pat. No. 4,957,424 is stated to combine two useful concrete pipe making technologies.
However, the concrete pipe making machines taught and suggested by U.S. Pat. No. 4,957,424 are not entirely satisfactory for several reasons. First, as seen in FIGS. 4 and 13 of said patent, the disclosed designs require that the vibrator be mounted below the motor that drives the counter rotating packerhead. Thus, the vibrator must be positioned substantially below the counter rotating packerhead. Because the design disclosed in U.S. Pat. No. 4,957,424 requires that the packerhead motors be disposed between the counter rotating packerhead and the vibrator, the combination of the counter rotating packerhead technology and vibrating technology is not as effective as it theoretically could be in terms of quality and speed of production.
The second and related problem associated with the design taught and suggested in U.S. Pat. No. 4,957,424 lies in the vibrator itself. The vibrator shown in FIGS. 4 and 13 are hydraulic vibrators. Because of the size of hydraulic vibrators generally, the vibrator must be disposed substantially below the lower roller assembly of the counter rotating packerhead. This placement further compromises the potential effectiveness of the general concept of combining a counter rotating packerhead with a vibrator. Ideally, strong vibrating forces should vibrate the concrete immediately after or concurrently with the application of the radially outward forming forces exerted by the counter rotating packerhead. By combining the action of the counter rotating packerhead with an immediate vibrating action, the entire pipe making process could be shortened. However, as disclosed in U.S. Pat. No. 4,957,424, the actions of the counter rotating packerhead and the vibrator are separate and distinct from one another due to the inherent structure of the hydraulic vibrator, thereby prolonging the pipe making process.
The third problem associated with the above-mentioned design can be best understood upon examination of FIG. 9 of U.S. Pat. No. 4,957,424. FIG. 9 represents an attempt to provide a compact drive system for a counter rotating packerhead to be disposed between the vibrator and counter rotating packerhead. Simply put, the two drive gears and multiple bearings disclosed in FIG. 9 are subject to the high amplitude vibrations provided by the vibrator disposed immediately beneath the motor. The result is a mechanically unreliable machine. Neither FIGS. 4 or 13 teach or suggest an isolation section to isolate the packerhead and its associated drive means shown in FIG. 9 from the vibrator. The only attempt or suggestion of isolation is provided by the plurality of shock absorbing pads mounted around the base that supports the drive means but this expedient has not been sufficient to cause the machine of U.S. Pat. No. 4,957,424 to go into use. In addition, only one pipe can be made at a time.
Thus, there is a need for an improved system in which a core vibrator may be disposed immediately below a counter rotating packerhead thereby providing a truly combined counter rotating packerhead/vibrator assembly, yet providing improved isolation from the working parts of the packerhead to a far greater degree than is presently provided. There is also a need for an improved drive shaft/drive system for a counter rotating packerhead that enables the drive means to be disposed in a remote location and isolated from the vibrator.
Still another problem associated with the prior art is the general lack of attempts to increase the rate of pipe making construction. The present invention contributes to this need in the art by providing a counter rotating packerhead assembly where the vibrator and counter rotating packerhead are disposed adjacent to one another for faster pipe making processes.
The present invention also discloses a pipe making machine with multiple cores and multiple forms so the machine makes at least two pipes of equal or different sizes at once, thereby increasing pipe productivity.